Method and system for treating wastewater

ABSTRACT

Treating distilled water with bacteria and other micro-organisms to remove nitrogen compounds from the distilled water. The distilled water may be produced from pretreating and distilling wastewater, such as wastewater from oil and natural gas production. The treatment steps of the distilled water include subjecting the water to microbial action under both anoxic and aerobic conditions and employing a membrane bioreactor to further purify the water. The purified water is still further purified by either reverse osmosis or ion exchange systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims priority under 35 U.S.C.§119 to U.S. Provisional Patent Application No. 61/662,801, titled“Methods and Systems of Wastewater Treatment,” filed Jun. 21, 2012. Thecomplete disclosure of this provisional patent application is herebyfully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods and systems for processingwastewater. More specifically, the present invention relates toprocessing wastewater, such as that generated when recovering oil andnatural gas, to produce a de-wasted water product meeting or exceedingbeneficial use criteria, such as the required properties of GeneralPermit WMGR123 (Pennsylvania Department of Environmental Protection,2012).

BACKGROUND OF THE INVENTION

Extracting oil and natural gas from unconventional resources, such asshale gas formations, through the combination of horizontal drilling andhydraulic fracturing has increased at a rapid pace in recent years. TheMarcellus Shale and Utica Shale are sedimentary formations that underliemost of Pennsylvania and West Virginia and extend into parts ofVirginia, Maryland, New York and Ohio. These shale formations are two ofseveral important gas reserves in the United States and together theyare one of the largest natural gas “plays” in the world. A “play” is thegeographic area underlain by a gas or oil containing geologic formation.

Development of these gas plays and other unconventional resourcespresents significant potential for economic development and energyindependence, but also presents the potential for environmental impactson land, water and air. For example, between 20% and 40% of the waterused for hydro-fracturing a gas well returns to the surface as flowback,and later as produced water. In addition to fracturing fluids added bydrillers, this wastewater picks up other contaminants from deep in theEarth.

In some parts of the United States, gas drilling companies typicallydispose of wastewater deep in the ground, by using deep injection wells.However, the geology in some locations, such as in Pennsylvania, doesnot necessarily allow for deep injections. Although municipal treatmentplants previously accepted this wastewater, certain states, such asPennsylvania, prevent water treatment facilities from processes waterthat has flowed back after fracturing. This restriction is thought topromote the goal of establishing and maintaining a closed loop processfor the recycling and reuse of oil and gas liquid wastes. States otherthan Pennsylvania also restrict the ability of publicly-owned treatmentworks to accept oil and gas wastewaters.

Recently, a number of states have passed regulations to treat processedwastewater having specific properties as a non-waste product. Forexample, General Permit WMGR123 (Pennsylvania Department ofEnvironmental Protection, 2012) identifies specific water qualitycriteria that, if met, will not require wastewater after it is processedto be treated as waste. The specific criteria of WMGR123 are reproducedbelow in Table 1.

TABLE I General Permit WMGR123 Property Limits Aluminum 0.2 mg/L Ammonia2 mg/L Arsenic 10 μg/L Barium 2 mg/L Benzene 0.12 μg/L Beryllium 4 μg/LBoron 1.6 mg/L Bromide 0.1 mg/L Butoxyethanol 0.7 mg/L Cadmium 0.16 μg/LChloride 25 mg/L COD 15 mg/L Chromium 10 μg/L Copper 5 μg/L EthyleneGlycol 13 μg/L Gross Alpha 15 pCi/L Gross Beta 1,000 pCi/L Iron 0.3 mg/LLead 1.3 μg/L Magnesium 10 mg/L Manganese 0.2 mg/L MBAS (Surfactants)0.5 mg/L Methanol 3.5 mg/L Molybdenum 0.21 mg/L Nickel 30 μg/L Nitrite -Nitrate 2 mg/L Nitrogen Oil & Grease ND pH 6.5-8.5 SU Radium-226 + 5pCi/L Radium-228 Selenium 4.6 μg/L Silver 1.2 μg/L Sodium 25 mg/LStrontium 4.2 mg/L Sulfate 25 mg/L Toluene 0.33 mg/L TDS 500 mg/L TSS 45mg/L Uranium 30 μg/L Zinc 65 μg/L

Accordingly, it is important that public health and the environment areprotected as unconventional resource extraction and productionactivities become a more prominent component of the oil and gas sector.To this end, regulations governing the management of such wastewaterhave been evolving at the state level, resulting in increased wastemanagement costs for the petroleum industry. Moreover, strict treatmenttarget requirements specified in each state for unrestricted-use waterare particularly challenging to meet. Aside from the challenges that maybe posed by the regulatory levels for certain contaminants, de-wastingwater from oil and natural gas production pose other challenges,including but not limited to the similar density of oil, mud and water;large fluctuation in daily flow rate of the wastewater; and highconcentrations of emulsified oil.

There is therefore a need in the art for methods and systems and forprocessing oil and gas wastewater with a goal to reuse the processedwater, such as for water used in well fracturing. It would be especiallybeneficial if such wastewater could be processed to produce de-wastedwater, i.e. unrestricted-use water that is not classified as a “residualwaste.” The production of de-wasted water would allow for lessburdensome storage, transportation, and reuse or the potential directdischarge of the water keeping it in the hydrologic cycle.

SUMMARY OF THE INVENTION

The present invention is generally directed to methods and systems fortreating wastewater, such as wastewater from producing oil and naturalgas and primarily directed to a process that employs bacteria and othertreatment processes to reduce the levels of contaminants in thewastewater to below regulatory criteria.

In one aspect of the present invention, a method for treating wastewateris provided. The method includes the steps of 1) seeding a pre-anoxictank with activated sludge comprising micro-organisms; 2) addingdistilled water comprising contaminants including nitrogen compounds tothe pre-anoxic tank, wherein the distilled water is produced fromtreated wastewater; 3) denitrifying the nitrogen compounds in the addeddistilled water in the pre-anoxic tank, wherein the denitrification isperformed by the micro-organisms under anaerobic conditions; 4)transferring the water from the pre-anoxic tank to an aeration tank;wherein additional nitrogen compounds in the water are nitrified underaerobic conditions wherein the nitrification is performed by themicro-organisms; 5) transferring the water from the aeration tank to apost-anoxic tank; wherein additional nitrogen compounds in the water aredenitrified under anaerobic conditions wherein the denitrification isperformed by the micro-organisms; and 6) transferring the water from thepost-anoxic tank to a membrane bioreactor comprising a membrane toremove a portion of the contaminants and micro-organisms from the waterto arrive at a purified water from the membrane bioreactor.

In another aspect of the present invention, a system for treatingwastewater is provided. The system includes a pre-anoxic tank in fluidcommunication with a distilled water source and operable to receivedistilled water from the distilled water source, where the distilledwater is produced from treated wastewater and further wherein thepre-anoxic tank includes activated sludge comprising micro-organisms; anaeration tank in fluid communication with the pre-anoxic tank andoperable to receive water treated in the pre-anoxic tank; a post-anoxictank in fluid communication with the aeration tank and operable toreceive water treated in the aeration tank; and a membrane bioreactorincluding a membrane, in fluid communication with the post-anoxic tankand operable to receive water treated in the post-anoxic tank, where thedistilled water includes contaminants such as nitrogen compounds and thenitrogen compounds are denitrified in the pre-anoxic tank andpost-anoxic tank and nitrified in the aeration tank; and where themembrane removes a portion of the contaminants and micro-organisms fromthe water to arrive at a purified water from the membrane bioreactor.

In yet another aspect of the present invention a method for treatingwastewater is provided. The method includes the steps of: 1) seeding apre-anoxic tank with activated sludge comprising micro-organisms; 2)controlling the temperature of distilled water comprising contaminantsincluding nitrogen compounds to a range of between 20° C. to 35° C.,wherein the distilled water is produced from treated wastewater; 3)filtering the distilled water to remove a portion of the contaminants;4) adding the filtered distilled water to the pre-anoxic tank; 5)denitrifying the nitrogen compounds in the added distilled water in thepre-anoxic tank, wherein the denitrification is performed by themicro-organisms under anaerobic conditions; 6) transferring the waterfrom the pre-anoxic tank to an aeration tank; wherein additionalnitrogen compounds in the water are nitrified under aerobic conditionswherein the nitrification is performed by the micro-organisms; 7)transferring the water from the aeration tank to a post-anoxic tank;wherein additional nitrogen compounds in the water are denitrified underanaerobic conditions wherein the denitrification is performed by themicro-organisms; 8) transferring the water from the post-anoxic tank toa membrane bioreactor comprising a membrane to remove a portion of thecontaminants and micro-organisms from the water to arrive at a purifiedwater from the membrane bioreactor; and 9) further processing thepurified water to satisfy a regulatory criterion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a schematic diagram of a wastewater treatment system inaccordance with an exemplary embodiment of the present invention.

FIG. 2 provides a block diagram of a wastewater treatment systemfollowing pretreating and distilling wastewater in accordance with anexemplary embodiment of the present invention.

FIG. 3 provides a schematic diagram of a wastewater treatment systemincluding biological treatment and membrane separation in accordancewith an exemplary embodiment of the present invention.

FIG. 4 provides a schematic diagram of a wastewater post-treatmentsystem including ion exchange in accordance with an exemplary embodimentof the present invention.

FIG. 5 provides a schematic diagram of a wastewater post-treatmentsystem including reverse osmosis in accordance with an exemplaryembodiment of the present invention.

FIG. 6 provides a schematic diagram of a wastewater treatment system inaccordance with an exemplary embodiment of the present invention.

FIG. 7 depicts a graph illustrating the chemical oxygen demand valuesfor the influent, effluent, and loading for an operation of a pilotplant in accordance with the wastewater treatment process depicted inFIG. 6 and employing ion exchange.

FIG. 8 depicts a graph illustrating the ammonia values for the influentand effluent for an operation of a pilot plant in accordance with thewastewater treatment process depicted in FIG. 6.

FIG. 9 depicts a graph illustrating the nitrate values for the effluentfor an operation of a pilot plant in accordance with the wastewatertreatment process depicted in FIG. 6.

FIG. 10 presents a process flow diagram for a wastewater treatmentprocess in accordance with an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention provides methods and systems for producing“de-wasted” water from oil and gas liquid wastewater. “De-wasted” wateris water with concentrations of contaminants belowregulatory-established criteria for the contaminants, such as thecriteria of General Permit WMGR123 (Pennsylvania Department ofEnvironmental Protection, 2012), provided in Table 1 above. The systemsand processes described herein may be employed to process wastewatercontaining contaminants, such as but not limited to, high totalsuspended solids (TSS), ammonia, nitrates/nitrites, chemical additives,high total dissolved solids (TDS), metals, and/or naturally occurringradioactive materials (NORM). For example, the treatment methods may beemployed to treat nearly any type of oil and gas wastewater, includingbut not limited to top-hole wastewater, pit wastewater, spent drillingfluids, flowback from hydraulic fracturing, and produced wastewater(e.g., by way of steam stimulation processes used for heavy oilrecovery).

FIG. 1 provides a schematic diagram of a wastewater treatment process100 in accordance with an exemplary embodiment of the present invention.Referring to FIG. 1, many aspects of the depicted process representconventional processes to arrive at a distilled water treatment productfrom wastewater from oil or natural gas production. As shown, incomingwastewater is transported from an oil or gas well site and/or associatedinfrastructure. For example, oil and gas wastewater may include liquidwastes from the drilling, development and/or operation of oil and gaswells and/or collection systems and facilities. In this exemplaryprocess, the wastewater is transported by a tanker 101 and is stored ina receiving water storage tank 102, until it is processed.Alternatively, wastewater may be added to receiving water storage tank102 directly through a direct pipe connection to the wastewater source.

The wastewater passes through one or more primary settling clarifiers103 and raw water storage tanks 104 before passing to a firstpretreatment train (items 105, 106, and 107) or second pretreatmenttrain (items 108, 109, 110, and 111). In a first pretreatment train, thepH of the waste water is adjusted in a pH adjustment/chemical additiontank 105. Once the pH is adjusted, the wastewater passes to a secondaryclarifier 106 before being sent to a final equalization tank 107.

In a second pretreatment train, the wastewater passes from the raw waterstorage tank 104 to a pH adjustment/chemical adjustment tank 108. Oncethe pH is adjusted, the wastewater enters one or more secondary lamellaclarifiers 109 before passing through a sand filter 110. The treatedwater is then stored in a final equalization tank 111. Materialcollected in the filter media of the sand filter 110 may be recycledback to the beginning of the first and/or second pretreatment trains forfurther processing.

Generally, solids entrained in the wastewater are removed from thewastewater at any of the primary settling clarifiers 103, secondaryclarifiers 106, and/or secondary lamella clarifiers 109. The solids arepassed to a sludge thickening tank (112 a, 112 b). The thickened sludgeis then passed through a filter press (113 a, 113 b) before it istransported (114 a, 114 b) for landfill disposal. The liquid removedfrom the solids in a sludge thickening tank (112 a, 112 b) may berecycled to the beginning of the first and/or second pretreatmenttrains.

Once the wastewater is passed through the first and/or secondpretreatment trains described above, it may be referred to as“pretreated water” and is sent to a pretreated water storage tank 115.Alternatively, the pretreated water may be held in a dedicatedpretreated water tank 116. Water stored in the pretreated water tank 116is designated for certain use without further processing by the presentinventive process.

The pretreated water that is to be further processed is passed from thepretreated water storage tank 115 to an ultrafiltration (UF) tank 117,where hydrostatic pressure forces the pretreated waste through asemipermeable membrane. Suspended solids and solutes of high molecularweight are retained in the membrane, while water and low molecularweight solutes pass through the membrane.

The pretreated water passes from the UF tank 117 to one or moredistiller units 118 such that “distilled water” is produced. In certainembodiments, a distiller unit 118 includes an evaporator, such as butnot limited to a NOMAD evaporator. Distilled water produced in thedistiller unit 118 is stored in a distilled water tank 119. As describedin greater detail below, in connection with FIG. 2, the distilled wateris passed to a de-wasting system 150 such that de-wasted water isproduced. The de-wasting system 150 includes the innovative processesand systems of the present invention.

As shown, in certain embodiments, a concentrated brine holding tank 120may be employed along with a mechanical brine crystallization unit 121to remove sodium chloride from wastewater to produce distilled water.The distilled water produced in the brine crystallization unit 121 isalso stored in the distilled water tank 119, and any concentrated brinemay be discarded or sold.

The processes described above that result in producing distilled waterfrom wastewater are typical processes used. Alternative processes may beemployed to pretreat and distill the wastewater to arrive at an inputwater product that is further processed by the systems and methods ofthe present invention. The present invention is not limited to theabove-described system and processes.

Although distilled water produced by the above described process may bereused in drilling, development and/or operation of oil and gas wellswithout further processing, it typically must still be treated as awaste product. Such waste must be stored in impoundments, tanks orcontainers that meet residual waste requirements prior to future use asmakeup water for hydraulic fracturing or other oil and gas welldevelopment activities. Accordingly, storage, transport, and reuse ofsuch a material may be burdensome and costly as compared to a non-wasteproduct. Further processing must be done to “de-waste” the water.

As shown in Table 2, below, distilled water produced by processingwastewater through a system similar to the system illustrated in FIG. 1,may not meet each of the criteria for a de-wasted water product, such asthe criteria listed in Table 1 which represent de-wasted water criteriafor Pennsylvania.

TABLE 2 Summary of Distilled Water Characteristics Nitrite/ AlkalinityTotal Ammonia Nitrate, Flow (mg/L TDS TSS COD CBOD₅ Nitrogen NH3—N NOx—N(MGD) pH CaCO₃) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) Average0.04 10.2 139 50 7 1257 439 47 31.9 0.25 Min. 0.002 8.1 134 6 5 211 8626 7.3 0.25  5% 0.006 9.7 135 13 5 234 112 30 15.2 0.25 25% 0.015 10.0137 21 5 363 222 37 24.6 0.25 50% 0.035 10.2 139 39 5 738 306 46 32.80.25 75% 0.051 10.4 142 75 6 1628 552 55 37.7 0.25 95% 0.095 10.6 144121 14 3404 958 63 55.1 0.25 Max 0.119 10.7 144 138 31 7900 1220 90 59.40.56

As shown in Table 2, the content of organic compounds in the water, asshown by the chemical oxygen demand (COD) value, are of particularimportance, as the values in Table 2 greatly exceed the limit for CODshown in Table 1. Organic compound concentrations may be determined byCOD and/or biological oxygen demand (BOD) values, which indicates themass of oxygen consumed per liter of solution. Another importantcontaminate when evaluating the distilled water against de-wasted watercriteria is nitrogen series contaminants, including ammonia (NH₃),nitrite, and/or nitrate.

Generally, ammonia, COD, and BOD concentrations in the distilled waterproduced from pretreating and distilling wastewater from oil and naturalgas operations as shown in FIG. 1 may be present at levels similar todomestic sewage. The median ratio of CBOD₅ to COD as shown in Table 2 isabout 0.5, which may be indicative of a fairly biodegradable wastewater.Moreover, the COD may consist of low molecular weight organics and/orvolatile organic compounds, as the organic materials passed through theUF tank 117.

The ammonia and total nitrogen concentrations of the distilled water mayalso be similar to domestic wastewater. As shown in Table 2, the totalnitrogen levels of a distilled water product produced from pretreatingand distilling wastewater from oil and natural gas operations may rangefrom about 20% to about 90% higher than ammonia levels. Because thenitrate/nitrite levels are shown to be low (e.g., about 0.25 mg/L), thetotal nitrogen and ammonia likely represent an organic nitrogenfraction, which may or may not be biodegradable.

FIG. 2 provides a block diagram of a wastewater treatment system 150following pretreating and distilling wastewater in accordance with anexemplary embodiment of the present invention. The illustrated system iscapable of producing de-wasted water meeting or exceeding each of thecharacteristics of a typical regulatory regime for de-wasted water, suchas Pennsylvania's WMGR123. Such a system solves many of the problems ofde-wasting distilled water, including but not limited to the similardensity of oil, mud and water; large fluctuation in daily flow rate; andhigh concentrations of emulsified oil.

Referring to FIGS. 1 and 2, distilled water, such as water stored in thedistilled water tank 119, passes into a temperature control unit 205,such as a heating or cooling system. The temperature of the influentdistilled water is preferably between 20° C. to 35° C. for the presentinvention to adequately treat the water. One or more temperature controlunits 205 are employed to either heat or cool the water to a temperaturewithin the preferred range. Water temperature instrumentation determinesthe water temperature of the inlet and outlet water from the temperaturecontrol units 205.

Once the temperature of the influent distilled water is within anacceptable range, the water passes through a pre-filter 210, such as butnot limited to a basket strainer or the like. The pre-filter 210 removesparticles from the water having a size of greater than about 1/20 inch,greater than about 1/16 inch, greater than about ⅛ inch, or greater thanabout ¼ inch. Solids collected in the pre-filter 210 (or generated insubsequent processes described below) may be managed in accordance withapplicable residual waste regulations.

The distilled water passes from the pre-filter 210 to one or more anoxicand aerobic tanks 220 to remove COD/BOD and nitrogen. Followingtreatment in the one or more anoxic and aerobic tanks 220, the treatedwater moves to one or more membrane separation tanks 230. The process ofanoxic and aerobic tanks 220 and membrane separation tanks 230 isdescribed in greater detail in connection with FIG. 3, below. Followingprocessing in the anoxic and/or aerobic tanks 220 and membraneseparation tanks 230, the processed water stream is further treated ineither an ion exchange system 240 or a reverse osmosis system 250. Theion exchange system 240 or a reverse osmosis system 250 are described ingreater detail below in connection with FIGS. 4 and 5, respectively.

FIG. 3 provides a schematic diagram of a wastewater treatment system 300including biological treatment and membrane separation in accordancewith an exemplary embodiment of the present invention. Referring toFIGS. 1, 2, and 3, a liquid water stream, such as the distilled waterstored in the distilled water tank 119, enters a pre-anoxic tank 310from the temperature control system 210 through pump 305, where adenitrification reaction occurs. Denitrification is a microbial processwhere nitrate (NO₃ ⁻) is converted to nitrite (NO₂ ⁻), which isconverted to nitric oxide and nitrous oxide (NO+N₂O), which is convertedto nitrogen gas (N₂). The liquid water stream is added to the tank in acontinuous process.

The pre-anoxic tank 310 is “seeded” with biological material thatincludes bacteria. The bacteria (e.g., heterotrophic bacteria) in thepre-anoxic tank 310 convert any nitrate compounds in the wastewater tonitrogen gas, which is released into the atmosphere. Althoughdenitrification releases nitrogen from the water, oxygen released in theprocess stays dissolved in the water, which reduces the oxygen inputneeded for the system in the next step of the process. The source of thebiological material is sludge from a sewage processing plant, typicallyreferred to as “activated sludge.” Activated sludge includes sludgeparticles produced in waste treatment by the growth of organisms inaeration tanks, such as in a sewage treatment plant. The sludge is“activated” because the sludge includes living material such asbacteria, fungi, and protozoa. These living material are used in thedenitrification reaction. This seed step occurs once, to seed the tank.Then, additional bacteria is grown as part of the COD degradationprocess. In some cases, all of the bacteria in the system may die. Inthat case, the system must be re-seeded.

In the embodiment of FIG. 3, the pre-anoxic tank 310 includes asubmersible mix pump 311 for mixing the tank contents. Optionally,additives such as but not limited to phosphorous may be added to thepre-anoxic tank 310. Phosphorus is an essential nutrient required forbiological treatment which is missing in the wastewater. For example,phosphorus, in the form of phosphoric acid stored in tank 358 is added,through pump 353, as needed to the influent of pre-anoxic tank 310.Typically, a dissolved oxygen level in the anoxic tank may be from aboutgreater than 1.0 mg/L and the temperature in the pre-anoxic tank 310range from about 20° C. to about 35° C. An industrial scale pre-anoxictank may be about 10,000 gallons of capacity, without limitation.

The distilled water being processed in process 300 passes from thepre-anoxic tank 310 to an aeration tank 320 such that nitrogen compounds(e.g., NH₃, NO₂) are nitrified by nitrifying bacteria. Nitrification isthe oxidation of ammonia with oxygen into nitrite followed by theoxidation of these nitrites into nitrates by biological mechanisms, suchas by bacteria or other micro-organisms. Under aerobic conditions,biological organisms (e.g., ammonia oxidizing bacteria and/or nitriteoxidizing bacteria) added in the pre-anoxic tank 310 and remaining inthe water that passes to the aeration tank 320 oxidize nitrogencompounds to nitrite and nitrate compounds.

Oxygen is added to the aeration tank 320, for example by employingcompressors and/or diffusers or by high purity oxygen and mechanicalsurface aeration. As shown in FIG. 3, an air pump 321 delivers air intothe aeration tank 320, and a pocket of compressed air forms in the topof the aeration tank 320. As water enters the tank from the pre-anoxictank 310, it passes through the air pocket. For example, the aerationtank 320 may contain a baffle or other structure, such that water spraysdown through the pocket of compressed air. Moreover, water may befurther aerated in the tank through a riser or the like (not shown). Forexample, coarse bubble diffusers may be submerged in the tank liquid andprovide air to the aeration tank 320.

An industrial scale version aeration tank 320 may be from about 50,000to about 75,000 gallons, without limitation. The tank may include a ventsystem (not shown) to release gasses that form in the tank and toprovide for a turnover of air in the tank. The pump 321 and vent may becontrolled by the same electrical circuit such that vent may open whenthe pump 321 is running, and the vent may close when the pump is turnedoff. Moreover, the pump 321 and vent circuitry may be in electricalcommunication with a pressure gauge so that they may be automaticallyoperated based on the pressure within the tank. In other embodiments,the pump 321 and vent circuitry may be in communication with a flowswitch, which turns the pump/vent system on when water is flowing.

As shown, any number of chemicals may be added to the aeration tank 320.Bacteria macronutrients, such as but not limited to phosphorous, may beadded at any point in the anoxic/aerobic biological treatment system.For example, phosphorus, in the form of phosphoric acid stored in tank358 is added, through pump 353, as needed, to aeration tank 320.

Micronutrients may be added by directing, for example, boiler or coolingtower blow-down to the system along with a source of alkalinity (e.g.,NaOH) for pH control, as nitrification consumes alkalinity. Thealkalinity source may be KOH, instead of or in addition to NaOH incertain embodiments, due to the very low Cl⁻ and Na⁺ limits forde-wasting water in some regulatory regimes, such as the limits shown inTable 1. For example, boiling or cooling tower blow-down from thetemperature control unit 205 with added NaOH or KOH is stored in tank357 and added by pump 353. Typically, antifoam agent addition may beneeded to control foaming, depending on the characteristics of thedistilled water. Accordingly, an antifoam agent stored in tank 356 maybe added to the aeration tank 320 by pump 351.

Nitrate may be recycled to the pre-anoxic tank 310 from the aerationtank 320 through a dedicated recycle pump 322 or the like. In this way,the oxygen requirement of the waste in the pre-anoxic tank 310 is met bythe release of oxygen from nitrates in the recycled flow.

The treated distilled water passes from the aeration tank 320 to apost-anoxic tank 330, where residual nitrate (e.g., from about 3 toabout 10 mg/L) is removed by microbial action. In some cases, the carbonconcentration in the water may be insufficient to support this microbialaction. In those cases, carbon is added from dosing the post-anoxic tank330 with a supplemental carbon source, such as ethanol, which is storedin tank 359 and delivered by pump 354. The use of a supplemental carbonsource may not be necessary in all cases. Such a source may be employeddue to low BOD/COD levels in the treated water. The amount of addedcarbon varies with the design influent loading, which can vary fromsystem to system. The amount of carbon in the system should besufficient to maintain bacterial growth, such as to prevent the bacteriafrom dying off and requiring the system to be re-seeded.

Denitrification requires a carbon source to take place. Althoughsufficient carbon may be available in the distilled water entering thepre-anoxic tank 310, the BOD:N ratio of the material entering thepost-anoxic tank 330 may be insufficient to allow for adequatedenitrification. Accordingly, an external source of carbon (e.g.,methanol, ethanol, etc.) may be added to the post-anoxic tank 330 toincrease the BOD:N ratio. Such addition may occur by way of a carbondosing pump or other means. The amount of added carbon must be carefullycontrolled, as too much added carbon introduces an unacceptable BOD intothe effluent, while too little leaves some nitrates under-nitrified.Process measurements, such as flow and COD loading, are taken todetermine the amount of carbon to be added.

The post-anoxic tank 330 may include the same or similar properties asthe pre-anoxic tank 310. For example, an industrial scale post-anoxictank may be about 10,000 gallons, without limitation. Moreover, thepost-anoxic tank 330 may include a submersible mix pump 331 for mixingof the tank contents.

It has been found that the particular arrangement of the pre-anoxic tank310, aeration tank 320, and post-anoxic tank 330 is beneficial, as thepre-anoxic tank 310 has the advantage of a higher denitrification ratewhile the nitrates remaining in the liquor passing out of the pre-anoxictank 310 can be denitrified further in the post-anoxic tank 330 throughendogenous respiration. However, other arrangements of anoxic/aerobictanks may be employed as desired or required. For example, any number ofaeration and anoxic tanks may be employed, and the order of such tanksmay be rearranged. In one alternative embodiment, the post-anoxic tank330 may be omitted. In that embodiment, treated water moves from theaeration tank 320 to the membrane separation system 340 (discussedbelow).

Membrane separation 230 (e.g., employing a membrane bioreactor or thelike) is employed to reduce both BOD/COD and nitrogen from the treatedwater that passed through the anoxic/aerobic biological treatment tanks220 (that is, through tanks 310, 320, and 330).

Suspended bacteria and other particulate solids (i.e., mixed liquor) maybe removed from the treated water using a membrane separation system340. There are many different options for a membrane separation system340 design, but a micro or ultrafiltration membrane bioreactor (“MBR”)is preferred to separate solids from treated effluent. Also, most of theCOD in the water is removed through microbial action in the MBR 340. Anexemplary MBR includes a submerged membrane 341.

In one specific embodiment, the MBR 340 includes a hollow-fiber membranehaving fibers held in modular cassettes that are immersed directly intoa liquid. Each cassette includes a permeate header that is connected tothe suction side of a reversible rotary lob pump, which applies a lowpressure vacuum to draw treated effluent through the microscopic poresof the fibers in an outside-in flow path. This approach may minimizeenergy demands and prevent particles from fouling and plugging insidethe membrane fiber. One particular MBR thought to be useful in theprocesses described herein is a Z-MOD™-L MBR manufactured by GE Water &Process Technologies. The Z-MOD™-L MBR includes a ZEEWEED® 500 membrane.

The MBR 340 includes the membrane cassette 341 and tank internals,membrane air scour blower 342, mixed liquor recycle pump 343, permeatepumps, chemical feed systems, a main control panel, and/or otherinstrumentation. The system may be scalable such that cassettes may beadded or removed as necessary.

The MBR 340 may have bacteria macronutrients, such as but not limited tophosphorous, added thereto. Micronutrients may be added by directingboiler or cooling tower blow-down to the system along with a source ofalkalinity for pH control (nitrification consumes alkalinity).Generally, antifoam addition may be needed to control foaming, dependingon the characteristics of the distilled water. For example, boiling orcooling tower blow-down from the temperature control unit 205 with addedNaOH or KOH is stored in tank 357 and added by pump 353. An antifoamagent stored in tank 356 may be added to the MBR 340 by pump 351.

Different scouring and cleaning systems may also be employed to keep themembranes 341 of the MBR 340 clean depending on the system design. Forexample, in a submerged membrane design, the membrane may be cleanedusing an air scour system 342. In certain embodiments, the MBR 340 maybe cleaned in place using caustic and/or citric acid solutions.Accordingly, parallel membrane tanks may be provided such that one tankcan be taken offline for cleaning without stopping treatment.

As shown, mixed liquor may be recycled from the membrane tank to thepre-anoxic tank 310 by way of the mixed liquor recycle pump 343. Therecycled material may be referred to as return activated sludge (RAS)and may be recycled to the pre-anoxic tank 310 to re-seed the newdistilled water entering the anoxic/aeration system. Excess wasteactivated sludge (WAS) may be removed from the system, such as throughvalve 355. Treated water passes from the MBR 340 to a storage tank 350.Although a treated water storage tank 350 is shown, this tank may beomitted and the permeate leaving the MBR 340 can be transferred directlyto an ion exchange system 240 and/or a reverse osmosis system 250.

Although permeate, or purified water, leaving the membrane separationsystem 340 may meet the limitations of Table 1, above, in certainsituations, additional processing may be required to further purify thewater. Referring back to FIG. 2, water leaving membrane separation 340may be introduced to an ion exchange system 240 and/or a reverse osmosissystem 250. These systems may be employed to reliably remove varyingconcentrations of NH₃—N and/or NO_(x)—N.

FIG. 4 provides a schematic diagram of a wastewater post-treatmentsystem 240 including ion exchange in accordance with an exemplaryembodiment of the present invention. In certain situations,heterotrophic bacteria may inhibit the growth and activity of nitrifyingbacteria to consume ammonia. In this situation, ion exchange offers analternative or additional method in the removal of ammonia ions. Ionexchange offers a number of advantages to biological treatment alone,including the ability to handle spikes in influent ammonia levels andthe ability to operate over a wider range of temperatures.

Referring to FIG. 4, water from the treated water storage tank 350 isintroduced to a strong acid (10 percent) cation (“SAC”) column 410.Although a treated water storage tank 350 is shown, this tank may beomitted and the permeate leaving the MBR 340 can be transferred directlyto the SAC column 410. The pH of water exiting the treated water storagetank 350 be adjusted by adding sodium hydroxide from a tank 405 by apump 407. The SAC column 410 includes an amount of H⁺ ions, which may beregenerated by the addition of, for example, H₂SO₄ or HCl. In oneembodiment, the SAC column may remove NH₃—N while reducing the pH of thewater to less than about 6.0. The SAC column includes about 50 cubicfeet of resin. The lifetime of the resin is about 24 hours before itmust be regenerated.

The SAC column 410 is typically operated until break-though. In oneexemplary embodiment, the SAC column 410 is actually two columnsarranged in series in a lead/lag configuration. In a lead/lag theprimary bed receives the contaminated water. This initial column thecontaminant or contaminants of concern, usually to acceptable levelsitself. The second column acts as a safeguard against contaminantsremaining in the water following break-through of the primary column.Upon break-through, the primary column is regenerated and placed backinto service, typically as the secondary column, with the secondarycolumn now becoming the primary column. In an alternative embodiment,the system 240 includes two or more sets of SAC columns 410 that operatein parallel, with each set including a primary and secondary column in alead/lag configuration. With a parallel arrangement, sets of columns canbe taken offline to regenerate without stopping the process.

The water passed from the SAC column 410 to a decarbonator 420 such thatCO₂ formed in the SAC column 410 may be removed from the water. Adecarbonator liberates CO₂ from the water to a gaseous state. Forexample, the decarbonator 420 may be a forced draft decarbonator. In aforced draft decarbonator, water is fed into the top of a packed towerat atmospheric pressure. The tower is typically packed with materialwith a very high surface contact area, which enhances the transfer ofCO₂ from the liquid phase to the gas phase. Air is forced up from thebottom of the packed tower in a counter-current flow design. The airbecomes saturated with CO₂ from contacting the water and is removed atthe top of the tower.

Treated water leaving the decarbonator 420 may be pH-neutralized 440 toa pH of from about 6.0 to about 8.0, preferably about 7.0.Neutralization may occur through a tank 405 having a base (e.g., NaOH)and optionally CO₂ (not shown) mixed into the water using a mixer 441.The neutralized water is then stored in a storage tank 450 for reuse.The levels of contaminants in the water are such that the stored wateris “de-wasted” water, such that it meets certain regulatory limits, suchas the Pennsylvania limits provided in Table 1.

FIG. 5 provides a schematic diagram of a wastewater post-treatmentsystem 250 including reverse osmosis in accordance with an exemplaryembodiment of the present invention. Water from the treated waterstorage tank 350 is introduced into a mixer 510 to adjust the pH of thewater. The pH of the water is adjusted to less than about 6.0 by adding,for example, H₂SO₄ or HCl stored in tank 502 and added by pump 503 andmixing in mixer 510. The pH adjustment step may be employed when theremoval of NH₃—N is required to ensure that NH₃—N remains as ions anddoes not enter the gaseous phase.

An anti-scalant additive stored in tank 506 may be added to thepH-adjusted liquid through pump 507, and then liquid passed through a 1micron pre-RO filter 515. The filtered liquid is then introduced to anreverse osmosis vessel 525 using a high pressure reverse osmosis feedpump 520.

The reverse osmosis vessel 525 forces water from a region of high soluteconcentration through a semipermeable membrane to a region of low soluteconcentration by applying a pressure in excess of the osmotic pressure.In certain embodiments, the reverse osmosis membrane(s) employed includea dense layer in the polymer matrix (e.g., skin of an asymmetricmembrane or an interfacially polymerized layer within athin-film-composite membrane). The membrane may be designed to allowonly water to pass through the dense layer, while preventing the passageof solutes. In one embodiment, the reverse osmosis includes a“sacrificial” member to increase recovery.

The reverse osmosis vessel 525 includes a number of modular “plug andplay” reverse osmosis skids having any number of thin-film compositereverse osmosis membranes. The system includes one or more trains havingmultiple membranes that may be added or removed based on the amount ofwater to be processed. In one specific example, thirty-six (36) reverseosmosis membranes may be employed.

The reverse osmosis vessel 525 include a clean-in-place (CIP) system530. The CIP system circulates cleaning liquids in a cleaning circuitthrough the reverse osmosis system. In certain embodiments the CIPsystem 530 may be skid-mounted. Through this cleaning process, trappedcontaminants are removed from the reverse osmosis vessel 525 membranes.

The trapped materials removed from the reverse osmosis vessel 525membranes may be recycled from the reverse osmosis vessel 525 to theanoxic/aerobic system 220 (see FIG. 2). Specifically, the trappedmaterials removed from the reverse osmosis system 525 membranes may beused to re-seed the pre-anoxic tank 310 or removed from the system aswaste or returned to the head of the pretreatment system (see FIG. 1).

Upon exiting the reverse osmosis vessel 525, the water may require pHelevation to ensure the pH is from about 6.0 to about 8.0, preferablyabout 7.0. To that end, the water may be passed through a pH adjustmentsystem, which may include a metering pump 505 controlled by a downstreampH probe and an inline flash mixer 535. A base, such as but not limitedto NaOH, may be added to the water from tank 501 and mixed with themixer 535.

The processed water may also require re-mineralization to preventcorrosion of downstream pipes, tanks, trucks, etc. As shown, brine froma brine tank 545 may be pumped using pump 547 and mixed into the water.The re-mineralized water is then stored in, for example, a pure waterstorage tank 540 before being shipped to an end user.

Either the ion exchange system 240 or the reverse osmosis system 250 maybe used to further treat the treated water that exits the MBR 340. Thedecision as to which system to employ may depend on economic factorsrather than technical factors.

Referring back to FIG. 2, effluent water exiting the ion exchange system240 b or reverse osmosis system 250 may meet or exceed each of therequired properties shown in Table 1, above. Accordingly, distilledwater having the properties of Table 2 may be passed through theillustrated processing steps to be transformed into de-wasted water. Incertain embodiments, the de-wasted water resulting from the abovedescribed treatment process may not be considered a waste as defined in25 Pa. Code §287.1. Moreover, the de-wasted water may be reused at oiland gas well sites such that a “closed loop” is created. In otherembodiments, the de-wasted water may be used in any number of otherapplications or may simply be discarded into the environment orotherwise handled as fresh water.

Distilled water having up to about 600 mg/L cBOD₅ may be processed usingthe methods described herein. The cBOD₅ level may be reduce to less thanabout 10 mg/L, less than about 5 mg/L, less than about 2.5 mg/L, or evenless than about 1 mg/L. Distilled water having influent COD levels ofless than about 8000 mg/L may be treated using the methods describedherein. Such COD levels may be reduced to less than about 20 mg/L, lessthan about 15 mg/L, less than about 10 mg/L, or even less than about 5mg/L in de-wasted water. In some embodiments, the COD levels of ade-wasted water may be reduced by from about 95% to about 99% or greateras compared to COD levels of influent distilled water.

In some embodiments, distilled water having influent NH₃—N levels of upto about 50 mg/L may be treated using the methods described herein. SuchNH₃—N levels may be reduce to less than about 2.0 mg/L, less than 1.5mg/L, less than 1.0 mg/L, or even less than about 0.5 mg/L. Similarly,the treatment methods may provide de-wasted water having effluentNO_(x)—N levels of less than about 2.0 mg/L, less than about 1.5 mg/L,less than 1.0 mg/L, or even less than about 0.5 mg/L from distilledwater having an influent NO_(x)—N level of up to about 0.6 mg/L.

The TSS levels of an exemplary de-wasted water produced subjected to thedescribed treatment methods may be from about 0.1 mg/L to less thanabout 5 mg/L. In an exemplary embodiment, the TSS levels of a de-wastedwater may be from about 0.5 mg/L to less about 2 mg/L, and moreparticularly less than about 1 mg/L. Such results may be obtained byprocessing distilled water having an influent TSS level of up to about15 mg/L, e.g., 10 mg/L or 5 mg/L.

In one exemplary embodiment, the system may be designed to handlemaximum flows and 75 percentile cBOD₅ and nitrogen concentrations, asshown in Table 2. Higher influent loadings may be managed throughequalization or diversion to a sewer. For example, the system may bedesigned to process up to about 300,000 gallons per day of distilledwater having a pH from about 8 to about 11. Exemplary systems arecompatible with distilled water having up to about 40 mg/L NH₃—N and upto about 60 mg/L total nitrogen at a temperature of from about 20 toabout 40° C.

Table 3, below, shows the influent parameters supported by an exemplarysystem according to the invention:

TABLE 3 Exemplary Influent Design Parameters for Biological SystemInfluent Parameters Average Maximum Design Basis Flow Rate (gpd) 126,000201,600 126,000 COD (mg/L) 750 1,250 2000 COD (lb/day) 788 2101 2101Total Nitrogen (mg/L) 70 75 120 Total Nitrogen (lb/d) 74 126 126 TotalPhosphorus (mg/L) <1 <1 <1 TSS (mg/L) 5 10 10 Alkalinity (mg/L) 260 260260 pH 8-11 Temperature 20-35° C.

Table 4, below, shows design parameters of an exemplary system accordingto the invention:

TABLE 4 Exemplary Design Parameters for Biological System Design DesignParameters Average Max Basis Anoxic Tank (gal) 15000 15000 15000 AerobicTank 1 (gal) 50000 50000 50000 Aerobic Tank 2 (gal) 50000 50000 50000Membrane Tanks (gal) 12230 12230 12230 HRT (h) 24.2 15.1 24.2 MixedLiquor Temp. (° C.) 20-34 20-34 20-34 Mixed Liquor Suspended Solids in8000 10000 10000 Aerobic Tank (mg/L) Mixed Liquor Volatile Suspended7420 9699 9810 Solids in Aerobic Tank (mg/L) Solids Retention Time (SRT)(d) 46.6 15.2 15.2 RAS Flow From Membrane Tank (Q) 4.0 4.0 4.0 SludgeWasting (gpd) (the excess 1730 @ 1% 5350 5300 @ growth that needs to beremoved @1.25% 1.25% from the system) Sludge Wasting/Influent Flow 1.4%2.7% 4.2% Diffusers Coarse Coarse Coarse Bubble Bubble Bubble MaxProcess Air Flow (scfm) 700 1490 1500 (for aeration tank)

Although any known methods may be employed to determine whether theresultant de-wasted water meets the limitations of Table 1, in oneembodiment, such a determination is made according to one or more of thefollowing:

-   -   (a) A minimum of 14 consecutive daily flow proportional        composite samples analyzed for strontium, barium and TDS;    -   (b) A minimum of 2 weekly flow proportional composite samples        which are taken a minimum of 7 days apart analyzed for all        constituents listed in Table 1 except ammonia, benzene,        methanol, and toluene; and    -   (c) A minimum of 2 grab samples taken a minimum of 7 days apart        analyzed ammonia, benzene, methanol, and toluene.

Moreover, once a de-wasted water is stored, it may be tested todetermine whether it continues to meet the limitations of Table 1, by:

-   -   (a) Collecting daily flow proportional composite samples and        analyzing them for strontium, barium and TDS;    -   (b) Collecting weekly flow proportional composite samples and        analyzing them for all constituents listed in Table 1 except        ammonia, benzene, methanol and toluene.    -   (c) Collecting weekly grab samples and analyzing them for        ammonia, benzene, methanol and toluene.        Of course modifications of the above testing methods may be        implemented if desired or required.

Analytical methodologies used to determine whether a de-wasted watermeets the requirements of Table 1 may include, but are not limited to,those in the Environmental Protection Agency's (“EPA”) “Test Methods forEvaluating Solid Waste, Physical/Chemical Methods” (EPA SW-846),“Methods for Chemical Analysis of Water and Wastes” (EPA 600/4-79-020),“Standard Methods for Examination of Water and Liquid Waste” (preparedand published jointly by the American Public Health Association,American Water Works Association, and Water Pollution ControlFederation), the Pennsylvania Department of Environmental Protection's“Sampling Manual for Pollutant Limits, Pathogens and Vector AttractionReductions in Sewage Sludge” or any comparable method subsequentlyapproved by the EPA or Department of Environmental Protection. Each ofthese documents is incorporated herein by reference in its entirety.

EXAMPLES

An exemplary pilot-sized distilled water processing system was testedwith an oil and gas liquid waste distillate. A schematic of the pilotsized plant 600 is illustrated in FIG. 6. As shown, the pilot plantincluded a 64 gallon pre-anoxic tank 610, a 210 gallon aeration tank620, a 65 gallon post-anoxic tank 630, a 90 gallon MBR 640, and an ionexchange system 645. The total volume of the pilot system was about 420gallons. Distilled water from tank 605 is pumped through strainer 607(<one-eighth inch mesh) to the pre-anoxic tank 610. The pre-anoxic tank610 includes a submersible pump 612 to mix the tank. Phosphorus, asphosphoric acid, is added from tank 614 to the pre-anoxic tank 610.

Treated water passed from the pre-anoxic tank 610 to the aeration tank620. Air is added to the aeration tank 620 using aeration blower 622.Nitrates are recycled from the aeration tank to the pre-anoxic tank 610by the nitrate recycle pump 624.

Treated water then passes to the post-anoxic tank 630. Carbon is addedusing a carbon source from tank 634 through carbon dosing pump 636. Thepost-anoxic tank 630 includes a submersible pump 632 to mix the tankcontents. A recycle pump 642 transferred the treated water into themembrane tank 640. Air from an aeration blower 644 is used to scour themembranes.

Permeate is sent from the membrane tank 640 through an ion exchangesystem 645 and into an effluent container 650. Pump 642 removes thepermeate from the membrane tank 640. Solids are removed to a batch WAScontainer 646 or gravity feed back to the pre-anoxic tank 610.

A seed sludge was obtained from a municipal sewage plant and screened toless than 3 mm before adding to the pre-anoxic tank 610 of the pilotplant. The pilot system was then operated with influent distilled waterfalling within the parameters shown in Table 2 above for approximately 2months for the bacteria in the process to acclimate to the specificwastewater characteristics and reach “steady state.” The pilot systemwas run multiple times from October 2011 to at least March of 2012, andthe performance of the system is shown graphically in FIGS. 7-9. FIG. 7depicts a graph 700 illustrating the chemical oxygen demand values forthe influent, effluent, and loading for an operation of a pilot plant600 in accordance with the wastewater treatment process depicted in FIG.6 and employing ion exchange. FIG. 8 depicts a graph 800 illustratingthe ammonia values for the influent and effluent for an operation of apilot plant 600 in accordance with the wastewater treatment processdepicted in FIG. 6. FIG. 9 depicts a graph 900 illustrating the nitratevalues for the effluent for an operation of a pilot plant 600 inaccordance with the wastewater treatment process depicted in FIG. 6.

Referring to FIG. 7, the COD concentration of the influent waterentering the pilot system and the effluent water exiting the pilotsystem are shown. Upon the addition of an ion exchange system to thepilot plant, the COD concentration of the effluent water was found to beconsistently less than about 20 mg/L.

Referring to FIG. 8, the NH₃—N concentration of the influent waterentering the pilot system and the effluent water exiting the pilotsystem are shown. Upon the addition of an ion exchange system to thepilot plant, the NH₃—N concentration of the effluent water was found tobe consistently less than about 2.0 mg/L.

Referring to FIG. 9, the NO₃—N concentration of the influent waterentering the pilot system and the effluent water exiting the pilotsystem are shown. Upon the addition of an ion exchange system to thepilot plant, the NO₃—N concentration of the effluent water was found tobe consistently less than about 2.0 mg/L.

FIG. 10 presents a process flow diagram for a wastewater treatmentprocess 1000 in accordance with an exemplary embodiment of the presentinvention. Referring to FIGS. 1, 2, 3, 4, 5, and 10, at step 1005, thepre-anoxic tank, such as pre-anoxic tank 310, is seeded with activatedsludge. This sludge includes bacteria and other micro-organisms thatremove nitrogen from a waste stream through microbial action.

At step 1010, a distilled water product enters a temperature controlsystem, such as temperature control system 205, where the temperature ofthe distilled water product is adjusted to between 20° C. to 35° C. Thedistilled water product may be the result of pretreating and distillingwastewater from oil and natural gas production. In some cases, thetemperature of the water will need to be increase to satisfy thetemperature range of between 20° C. to 35° C. In most cases, thetemperature will need to be lowered. In still some cases, thetemperature of the distilled water product will be within the desiredtemperature range without adjustment.

At step 1015, the distilled water product is pre-filtered, or screened,to remove solids from the distilled water. Such as by pre-filter system210. The screen mesh size ranges from a mesh size capable of removingparticles of at least 1/20 inch in size to a mesh size capable ofremoving particles greater than about ¼ inch in size.

At step 1020, the distilled water product is introduced into thepre-anoxic tank. Once in the tank, microbes contained in the tank digestnitrogen-containing compounds in a denitrification process underanaerobic conditions. Phosphorus, such as in the form of phosphoricacid, may be added to the pre-anoxic tank to provide nutrients for themicro-organisms. Nitrogen gas is released out of the pre-anoxic tank.

At step 1030, the water treated in the pre-anoxic tank is transferred toan aeration tank, such as aeration tank 320, where nitrogen compoundsare nitrified by bacteria under aerobic conditions. Air is provided tothe tank to facilitate the microbial action. Nitrates from the aerationtank are recycled to the pre-anoxic tank.

At step 1040, the water treated in the aeration tank is transferred to apost-anoxic tank, such as post-anoxic tank 330, to remove residualnitrate by denitrification. If necessary, additional carbon is added tofacilitate the nitrate removal process. Micro-organisms in the waterperform the denitrification under anaerobic conditions.

At step 1050, the water treated in the post-anoxic tank is transferredto a membrane separator, such as membrane bioreactor 340. At this step,microbial action continues on the input side of the membrane. Thetreated water is forced through the membrane, removing themicro-organisms and other solids from the treated water. Thepermeate—the purified water that has passed through the membrane—iscollected for further treatment.

At step 1060, the permeate from the membrane bioreactor is furthertreated in a reverse osmosis system or an ion exchange system.

At step 1065, the membrane of the membrane bioreactor is scoured by airto remove the trapped materials, which may be recycled into thepre-anoxic tank as a source of activated sludge.

At step 1070, the water treated in the reverse osmosis system or ionexchange system is collected and tested to demonstrate compliance withde-wasted water criteria. The water, once demonstrated to be de-wastedwater, may be reused.

It is understood by those skilled in the art that the drawings arediagrammatic and that further items of equipment such as reflux drums,pumps, vacuum pumps, temperature sensors, pressure sensors, pressurerelief valves, control valves, flow controllers, level controllers,holding tanks, storage tanks, and the like may be required in acommercial plant.

We claim:
 1. A method for treating wastewater comprising the steps of:seeding a pre-anoxic tank with activated sludge comprisingmicro-organisms; adding distilled water comprising contaminantsincluding nitrogen compounds to the pre-anoxic tank, wherein thedistilled water is produced from treated wastewater; denitrifying thenitrogen compounds in the added distilled water in the pre-anoxic tank,wherein the denitrification is performed by the micro-organisms underanaerobic conditions; transferring the water from the pre-anoxic tank toan aeration tank; wherein additional nitrogen compounds in the water arenitrified under aerobic conditions wherein the nitrification isperformed by the micro-organisms; transferring the water from theaeration tank to a post-anoxic tank; wherein additional nitrogencompounds in the water are denitrified under anaerobic conditionswherein the denitrification is performed by the micro-organisms; andtransferring the water from the post-anoxic tank to a membranebioreactor comprising a membrane to remove a portion of the contaminantsand micro-organisms from the water to arrive at a purified water fromthe membrane bioreactor.
 2. The method of claim 1 further comprising thestep of further processing the purified water from the membranebioreactor in one of a reverse osmosis system or an ion exchange system.3. The method of claim 2 further comprising the step of testing thewater produced from the further processing of the permeate from themembrane bioreactor in one of a reverse osmosis system or an ionexchange system to demonstrate that the water is de-wasted and whereinthe treated wastewater comprises water from oil and natural gasproduction.
 4. The method of claim 1 wherein the temperature of thedistilled water added to the pre-anoxic tank is adjusted to the range ofbetween 20° C. to 35° C. prior to adding the distilled water to thepre-anoxic tank.
 5. The method of claim 1 further comprising the step ofpre-filtering the distilled water added to the pre-anoxic tank prior toadding the distilled water to the pre-anoxic tank to remove a portion ofcontaminants comprising suspended solids from the distilled water. 6.The method of claim 1 wherein phosphorus is added to the pre-anoxic tankto facilitate the denitrification of the nitrogen compounds in thedistilled water added to the pre-anoxic tank.
 7. The method of claim 1further comprising the step of recycling nitrates from the aeration tankto the pre-anoxic tank, wherein the nitrates are formed during thedenitrification of the additional nitrogen compounds.
 8. The method ofclaim 1 wherein contaminants and micro-organisms are trapped in themembrane and further wherein the trapped contaminants andmicro-organisms are collected and added to the pre-anoxic tank.
 9. Themethod of claim 1 wherein the permeate is tested to demonstratecompliance with a regulatory criterion.
 10. The method of claim 1further comprising the step of adding a carbon source to the post-anoxictank.
 11. A system for purifying wastewater comprising: a pre-anoxictank in fluid communication with a distilled water source and operableto receive distilled water from the distilled water source, wherein thedistilled water is produced from treated wastewater and further whereinthe pre-anoxic tank comprises activated sludge comprisingmicro-organisms; an aeration tank in fluid communication with thepre-anoxic tank and operable to receive water treated in the pre-anoxictank; a post-anoxic tank in fluid communication with the aeration tankand operable to receive water treated in the aeration tank; and amembrane bioreactor comprising a membrane, in fluid communication withthe post-anoxic tank and operable to receive water treated in thepost-anoxic tank, wherein the distilled water comprises contaminantsincluding nitrogen compounds and the nitrogen compounds are denitrifiedin the pre-anoxic tank and post-anoxic tank and nitrified in theaeration tank; and wherein the membrane removes a portion of thecontaminants and micro-organisms from the water to arrive at a purifiedwater from the membrane bioreactor.
 12. The system of claim 11 furthercomprising a post-treatment system operable to process the purifiedwater from the membrane bioreactor and comprising one of a reverseosmosis system or an ion exchange system.
 13. The system of claim 11further comprising a temperature controller operable to adjust thetemperature of the distilled water received by the pre-anoxic tank tothe range of between 20° C. to 35° C. prior to adding the distilledwater to the pre-anoxic tank.
 14. The system of claim 11 furthercomprising a pre-filtering module operable to filter the distilled waterreceived by the pre-anoxic tank prior to adding the distilled water tothe pre-anoxic tank to remove a portion of contaminants comprisingsuspended solids from the distilled water.
 15. The system of claim 11further comprising a phosphorus source operable to be add phosphorus tothe pre-anoxic tank to facilitate the denitrification of the nitrogencompounds in the distilled water added to the pre-anoxic tank.
 16. Thesystem of claim 11 further comprising nitrate recycle pump operable totransfer nitrates from the aeration tank to the pre-anoxic tank, whereinthe nitrates are formed during the denitrification of the additionalnitrogen compounds.
 17. The system of claim 11 further comprising amembrane scouring system, wherein the membrane scouring system removescontaminants and micro-organisms trapped in the membrane
 18. The systemof claim 17 further comprising a pump for returning the removedcontaminants and micro-organisms to the pre-anoxic tank.
 19. The systemof claim 11 further comprising a carbon source operable to be added tothe post-anoxic tank.
 20. A method for treating wastewater comprisingthe steps of: seeding a pre-anoxic tank with activated sludge comprisingmicro-organisms; controlling the temperature of distilled watercomprising contaminants including nitrogen compounds to a range ofbetween 20° C. to 35° C., wherein the distilled water is produced fromtreated wastewater; filtering the distilled water to remove a portion ofthe contaminants; adding the filtered distilled water to the pre-anoxictank; denitrifying the nitrogen compounds in the added distilled waterin the pre-anoxic tank, wherein the denitrification is performed by themicro-organisms under anaerobic conditions; transferring the water fromthe pre-anoxic tank to an aeration tank; wherein additional nitrogencompounds in the water are nitrified under aerobic conditions whereinthe nitrification is performed by the micro-organisms; transferring thewater from the aeration tank to a post-anoxic tank; wherein additionalnitrogen compounds in the water are denitrified under anaerobicconditions wherein the denitrification is performed by themicro-organisms; transferring the water from the post-anoxic tank to amembrane bioreactor comprising a membrane to remove a portion of thecontaminants and micro-organisms from the water to arrive at a purifiedwater from the membrane bioreactor; and further processing the purifiedwater to satisfy a regulatory criterion.